Select the postulate that states a line is determined by two points.
1. postulate 1: a line contains at least two points.
2. postulate 1a: a plane contains at least three points not all on one line.
3. postulate 1b: space contains at least four points not all on one plane.
4. postulate 2: through any two different points, exactly one line exists.
5. postulate 3: through any three points that are not one line, exactly one plane exists.
6. postulate 4: if two points lie in a plane, the line containing them lies in that plane.
7. postulate 5: if two planes intersect, then their intersection is a line.